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From Joseph Brennan <>
Subject Re: Points for missing MX Records
Date Thu, 24 Feb 2011 14:43:24 GMT

Multiple comments ...

> I just want Spamassassin to check if there is a MX Record in DNS for
> the sender.

I have no sense of how productive this would be.  Have you looked up
a good sample of sender domains and found that spammers are significantly
less likely to have an MX?  That would make it interesting to check.

> It would  also be cool if Spamassassin could compare senderdomain
> and helo name.

Helo should match the hostname, but that's all.  There are many
instances where the sender address is a different domain.  Vanity
domains, third-party mailings, and merged companies lead the list.
Much of it is legitimate mail.  Check any online bank or credit
statements you might have, for example.

> reject_unknown_sender_domain
>  Reject the request when Postfix is not final destination for the sender
> address, and the MAIL FROM address has no DNS A or MX record,

I assume that, like Sendmail, it has already converted CNAMEs
when it does this test.  Sendmail rejects for having none of MX, A,
or AAAA.  That hits 3% of mail thrown at our system.

> The problem, is that a MX record is NOT required for a sending host.

Who proposed checking that?  The question was about checking for an
MX record for the sender address, not the host.

Joseph Brennan
Columbia University Information Technology

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